Process for preparing a plastic film

ABSTRACT

A process for preparing a plastic film of controlled curl comprising blowing hot moistened air onto the surface of said plastic film.

United States Patent [1 1 Aono et al.

[111' 3,805,402 1 Apr. 23, 1974 PROCESS FOR PREPARING A PLASTIC FILM[75] Inventors: Masazumi Aono; Goro Uehara, both of Kanagawa, Japan [73]Assignee: Fugi Photo Film Co., Ltd.,

Kanagawa, Japan 22 Filed: Aug. 26, 1971 21 Appl. No.: 175,248

[30] Foreign Application Priority Data Aug. 26, 1970 Japan 45-74739 [52]US. Cl 34/23, 34/26, 34/30, 34/46, 34/50, 34/151 [51] Int. Cl. F26b 3/00[58] Field of Search 264/235, 346; 34/22, 23,

CURLING VALUE (K) Primary ExaminerCarroll B. Dority, Jr.

Assistant Examiner-Larry I. Schwartz Attorney, Agent, or Firm-Sughrue,Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A process for preparing aplastic film of controlled curl comprising blowing hot moistened aironto the surface of said plastic film.

10 Claims, 4 Drawing Figures 'ggggmummnv 0.5 Kg STEAM/Kg, DRY AIR) ggomumnm 0.2Kg STEAM/Kg DRY AIR) PMEHI'EH km 2 3 m4 mum; VALUE W W m A v mW "M II. [I M M A A E E V g m m M 0 W m m m m M U W "My W 59 6 4 2 c; w3@5413 FIG. 3

5! BLOWING TIME (MINUTES) 7oc-02 Kg STEAM/Kg DRY AIR 150c-2.0 KgSTEAM/Kg DRY AIR L 2 4 6 CURLINGV VALUE (K55) :55: I? was @223 s 225%BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to a process for preparing plastic films. Moreparticularly, the present invention relates to a process for controllingthe curl of a plastic film to a desired extent.

2. Description of the Prior Art Cellulose esters, for example, cellulosenitrate, cellulose acetate, cellulose propionate, cellulose butyrate,and mixed esters thereof, are generally manufactured into a film base bya casting method. It is known that plastic films obtained by saidprocess have some extent of curl. And the extent of curl (curling value)varies depending on the variation of the humidity of the atmosphere.

It is considered that this variation of curling value is due to the factthat the density and plasticizer have certain distributions along thedirection of film thickness. These distributions vary as conditions offilm formation change, and accordingly, change the curling value; thus,the change of curling value presents a serious hindrance in the case ofchanging the condition of the film casting and drying process.

It is also well known that, in the process for preparing photographicfilms, if a silver halide photographic emulsion is applied to one sideof said film, the film curls to the side of the emulsion layer becauseof the tension which is generated in the emulsion layer during thedrying step of said emulsion layer.

To prevent the curls which occur due to the many causes asabove-mentioned, some processes have been hitherto employed such as aprocess to balance the curl of the emulsion layer with a curl of agelatin layer applied on the other side of the film; a process to applysome layers of certain substances other than gelatin in order to achievethe curling balance corresponding to the swelling or shrinking of theemulsion layer during the developing step; and a process to apply alayer which balances the curl corresponding to the swelling or shrinkingof the emulsion layer during development and may be removed during thatstep.

There are also processes of curling the film base to the side oppositethe emulsion layer in advance in order to balance the curling value ofthe film. For example, a process of curling the film base to the sideopposite the emulsion layer by applying a swelling material thereto(such as acetone, for cellulose triacetate) and then drying the layer;and a process of curling the support to the other side opposite emulsionlayer by lowering the speed of drying the back layer in a drying step ofthe undercoating layer and back layer, which are applied before theapplying of the emulsion, are known, as well as other processes.

These processes, however, are not desirable industrially, because ofaccompanying defects such as the limited range of curl controlling, theincrease of thickness of the layers, or the increase of drying steps ofthe layers.

The aim ofthe present invention is to provide a process for overcomingsaid defects and for controlling the curl of plastic films with a simpletreatment.

aim, the present inventors have found out that a very industriallyfavorable result can be obtained when one prescribes three forconditions the humidty, the temperature and the blowing time of moisthot air that is blown onto the film; in order to control the curlingvalue (K) and the variation of the curling value (A K), depending on thechange of humidity of the air.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a piece of filmindicating the method to measure the curl.

FIG. 2 is a graph which shows the relation between humidity and thecurling value.

FIG. 3 is a graph which shows the relation of the curling value,humidity and times in Example 1.

FIG. 4 is a graph which shows the relation between the curling value andthe variation of the curling value with humidity in Example 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Said aim can be attained byblowing moist hot air, which is adjusted in temperature and humidity,for a fixed time onto the concave plastic film surface which is to becurled.

The higher the temperature and humidity of the moist hot air are, thelarger the results are; and the longer the blowing time is, the moreeffective the process is. These three factors can be combined suitablyaccording to the conditions of the respective processes.

For example, if a short time process is emphasized, the temperature andhumidity should be higher; and if making the error of curlingvalue smallis emphasized, the humidity should be lower and the time longer.

The desirable range of temperature is from 40 C to the point where thefilm begins to soften (softening point), and the desirable humidity ishigher than that corresponding to the dew point at 40 C (10 vol. percenthumidity). Of course, even if the temperature and the humidity are outof said ranges, the aim of the present invention can be attained bycontrolling the blowing time. I

It is desirable to treat each of the: films under the followingconditions:

Film Temperature Humidity Fixed time rang (C) range Vol. range (sec.)

Cellulose ester film 60 150 I0 I00 5 600 Celluose triacetate film 150 105 300 Polyethylene terephthalate 100 200 40 I00 l0 I200 Cellulose ester,used as a support for photography, is formed into a film by a castingmethod, sothe film contains residual solvent. Although the processaccording to the present invention is also effective when films containmuch residual solvent, the effect is greater when the amount of residualsolvent is less.

The curling value of the plastic film which is processed according tothe process of the present invention once,.seems to change superficiallyas the film is exposed to severe changes of humidity and temperatureduring the developing process.

It has, however, been determined that the degree of curl does notdecrease, but remains to the last.

It is also well known that the curling value of a film which is formedby a solution process varies according to the change of humidity of theatmosphere.

The above phenomenon results from the fact that differences occur in thedistribution of dope density and that of plasticizer along the directionof thickness of the finished film because the film is dried only fromone side when the dope is applied on the surface of an applicatingcasting velt. Therefore, the variation of curling (A K) due to humidityvariation is almost fixed by the drying conditions on the surface of thecasting velt. If this A K can be varied as is desired, a very favorableeffect can be sometimes obtained. For example, if a film is desired toremain flat regardless of the humidity of the atmosphere, the dependenceof the film on the humidity had better be small, and as for a filmsupport for a photographic element, a great dependence, of curling tothe other side, on humidity is desired in order to cancel the curl dueto moistening and swelling the gelatin film, as the film suffers anextremely great change of humidity during the developing process.

As is stated above, the control of curl of a plastic film according tothe present invention permits a suitable combination of temperature,humidity and time of blowing moist hot air according to each condition.Further, combining these three factors suitably, one can produce filmshaving the variations of the curling value (A K) different from oneanother in spite of having the same curling value.

It is known that to make A K large, a long time process with lowtemperature is more effective than a short time process with hightemperature and high humidity. As is stated above, it is very favorableto be able to vary the dependence of curling value on humidity,considering films as photographic supports.

As is stated above, a desired curling value can be obtained by thecontrol of curl of plastic films according to the present invention,selecting temperature, humidity and time of blowing moist hot airsuitably. Moreover, thecurling value variation depending on thevariation of humidity of the atmosphere can be varied by the combinationof these three factors. The process according to the present inventionis simpler, cheaper and more stable than processes hitherto known.

and a humidity of 0.2 or 0.5 kg steam/kg dry air, was blown at thesurface of a cellulose triacetate film having a thickness of 140 micronsand a curling value of 0 whishsyt ass w s d red Q. b curled concave forvarious periods. After drying said film at 105C for eight hours, 3 X mmpieces of said film (cf. FIG. 1) were cut out to measure the curl. Afterleaving the pieces in the atmosphere at 23C, 55% RH (Relative Humidity)for more than 24 hours, the curling values of these pieces of film weremeasured. The results are shown in FIG. 3. FIG. 3 shows that a highertemperature, a higher humidity and a longer blowing time yield a greatereffect.

To get the curling value 1, 60 seconds of blowing were required at 60Cand 0.08 Kg steam/Kg dry air. but only one second was required at 150Cand 10.0 Kg steam/Kg dry air. As is seen above, if a short'time processis emphasized, temperature and humidity should be high, and if makingerrors in curling values small is emphaszied, low temperature, lowhumidity and long blowing time should be favored.

Similar results can be obtained with other cellulose esters, that is,esters or mixtures of esters of nitric acid, acetic acid, propionicacid, butyric acid and the like.

EXAMPLE 2 Polyethylene terephthalate film, having a thickness of 100micro secs. and stretched three times biaxially by the fusion process offilm formation was processed in the same way as in Example 1. By blowingair at 140C and 5 Kg steam/Kg dry air for600 seconds, the

It has also been confirmed that the control of curl of film surface hada curling value of 1.

Effects of curling differ according to the kind and thickness ofpolymers. Desirable curl can be obtained by selecting suitabletemperature, humidity and time.

Similar results were obtained with other plastic films, that is,polyvinyl chloride, polystyrene, and the like.

EXAMPLE 3 Cellulose triacetate was dissolved in a mixture of so]- ventsconsisting chiefly of methylene chloride. A plasticizer was added to theresulting solution to obtain a dope. The dope, having a concentration of20.0 wt. was flowed onto the surface of a support. The prepared film wasstripped from the surface of the support when 25 wt.% of the solventremained in the film, and was introduced into a drying chamber.

In succession to the above step, when the residual solvent in the filmreduced to 20.0 wt.%, the surface of the film opposite to the supportwas treated by the process according to the present invention and thefilm EXAMPLE 1 5 dried. The results obtained are shown in the followingMoist hot air having a temperature of C or 130C t bl Residual solventProcess conditions Curling At the value time of After curl to theprocess drying Humidity* casting velt No. (wt (wt Temp (C) Time (sec.)side) From this, it can be seen that the process is effective whenresidual solvent remains in the film, (cf. No. 1 and No. 3). However,the effect is smaller, compared with when a small amount of residualsolvent remains. (cf. No. l and No. 2)

EXAMPLE 4 Cellulose triacetatefilm. having a thickness of 140 micronswas processed under two conditions,"( 1) 70C and 0.2 Kg steam/Kg dryair, and (2) 150C and 2 Kg steam/Kg dry air, with the time being varied,in the same way shown in Example 1. The curling values of the processedfilms were measured at 23C, and 25,55 and 85% RH (these values beingdenoted by K K K respectively). By taking the variation K (AK=K -K asthe ordinate, and K as abscissa, the relationship is shown in FIG. 4.

As is seen above, if the curling value (K of the processed film is thesame, the variation of the curling value (AK) due to humidity variationcan be changed. it can be seen that the process with low temperature andlow humidity is more effective than the process with high temperatureand high humidity to make the variation of the curling value (AK) due tothe humidity variation range.

What is claimed is:

1. in a process for preparing a plastic film of controlled curl usefulas a support for a photographic materialcomprising producing saidplastic film and treating it to control the curl thereof, theimprovement comprising controlling the curl by blowing hot moistened aironto the surface of said plastic film for a period of time sufficient toobtain a plastic film of desired curl.

'2. The process of claiml wherein the plastic film is a cellulose ester,polyvinyl chloride, polystyrene or polyethylene terephthalate film.

3. The process of claim 2 wherein said cellulose ester is cellulosenitrate, cellulose acetate, cellulose propionate, cellulose butyrate ora mixture theseof.

4. The process of claim 1 wherein the hot moist air, adjusted intemperature and humidity, is blown for a fixed time onto the plasticfilm surface, said surface being concave.

5. The process of claim 4 wherein the temperature is 1 within the rangeof from 40C to the softening temperature of the film.

6. The process of claim 4 wherein the humidity is more than the dewpoint at 40C.

7. The process of claim 4 wherein the time varies from 1 second to 1200seconds.

8. The process of claim 2 wherein the air, at a temperature of from 60C.to C..a:nd having a humidity of from 0.1 to 1 kilogram of steam perkilogram of dry air, is blown onto the surface of said cellulose esterfilm for a period of time of from 5 seconds to 600 seconds.

to 1,200 seconds.

1. In a process for preparing a plastic film of controlled curl usefulas a support for a photographic material comprising producing saidplastic film and treating it to control the curl thereof, theimprovement comprising controlling the curl by blowing hot moistened aironto the surface of said plastic film for a period of time sufficient toobtain a plastic film of desired curl.
 2. The process of claim 1 whereinthe plastic film is a cellulose ester, polyvinyl chloride, polystyreneor polyethylene terephthalate film.
 3. The process of claim 2 whereinsaid cellulose ester is cellulose nitrate, cellulose acetate, cellulosepropionate, cellulose butyrate or a mixture theseof.
 4. The process ofclaim 1 wherein the hot moist air, adjusted in temperature and humidity,is blown for a fixed time onto the plastic film surface, said surfacebeing concave.
 5. The process of claim 4 wherein the temperature iswithin the range of from 40*C to the softening temperature of the film.6. The process of claim 4 wherein the humidity is more than the dewpoint at 40*C.
 7. The process of claim 4 wherein the time varies from 1second to 1200 seconds.
 8. The process of claim 2 wherein the air, at atemperature of from 60*C. to 150*C. and having a humidity of from 0.1 to1 kilogram of steam per kilogram of dry air, is blown onto the surfaceof said cellulose ester film for a period of time of from 5 seconds to600 seconds.
 9. The process of claim 8 wherein the film comprisescellulose triacetate and wherein the air has a temperature of from 80*C.to 150*C.
 10. The process of claim 2 wherein the air, at a temperatureof from 80*C. to 200*C. and having a humidity of from 0.4 to 1 kilogramof steam per kilogram of dry air, is blown onTo the surface of thepolyethylene terephthalate film for a period of time of from 10 secondsto 1,200 seconds.